Which organic compounds are often used to create fragrances for the perfume industry

The organic compound often used in perfumes are ESTERS which are sweet smelling substances,  they give the sweet smell to fruits also. 

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.